A Butterfly-Shaped Gland in Your Neck Sets How Fast Your Cells Burn Fuel
Tell endocrine glands from exocrine glands and learn what a hormone is, locate the pancreas, thyroid, adrenal and pituitary glands, and see what insulin, glucagon and thyroxine do and what happens when there is too little or too much.
How do hormones control the body without using nerves?
Nerves send fast electrical messages along fixed paths. The endocrine system sends chemical messages through the blood instead. They travel more slowly but reach every part of the body, and their effects can last for hours, days or years — controlling growth, blood sugar and the rate at which cells use energy.
This part covers glands and hormones, where four major glands lie, and the hormones of the pancreas and thyroid with their disorders.
This part covers glands and hormones, where four major glands lie, and the hormones of the pancreas and thyroid with their disorders.
What is the difference between endocrine and exocrine glands, and what is a hormone?
Exocrine glands release their secretions through ducts, while endocrine glands have no ducts and release hormones straight into the blood; a hormone is a chemical messenger made in small amounts that acts on a distant target organ.
Exocrine glands
- Have ducts that carry secretions to a surface or cavity
- Examples: salivary glands, sweat glands, gastric glands
Endocrine glands
- Ductless; secretions pass directly into the blood
- Examples: thyroid, pituitary, adrenal glands
Mixed glands do both. The pancreas sends digestive juice along a duct to the intestine, and also releases hormones into the blood.
A hormone:
- Is secreted by an endocrine gland in very small amounts
- Is carried by the blood to a target organ
- Acts more slowly but for longer than a nerve impulse
An everyday example. A relative with diabetes who injects insulin is supplying a hormone their own pancreas cannot make enough of.
The substance. A hormone affects only cells that can recognise it, which is why one hormone in the blood can change the liver but not the skin.
Exocrine glands
- Have ducts that carry secretions to a surface or cavity
- Examples: salivary glands, sweat glands, gastric glands
Endocrine glands
- Ductless; secretions pass directly into the blood
- Examples: thyroid, pituitary, adrenal glands
Mixed glands do both. The pancreas sends digestive juice along a duct to the intestine, and also releases hormones into the blood.
A hormone:
- Is secreted by an endocrine gland in very small amounts
- Is carried by the blood to a target organ
- Acts more slowly but for longer than a nerve impulse
An everyday example. A relative with diabetes who injects insulin is supplying a hormone their own pancreas cannot make enough of.
The substance. A hormone affects only cells that can recognise it, which is why one hormone in the blood can change the liver but not the skin.
Where exactly are the pancreas, thyroid, adrenal and pituitary glands, and what shape is each?
The pancreas is a long leaf-shaped gland in the loop of the duodenum below the stomach, the thyroid is a butterfly-shaped gland in the neck, the adrenals are cap-like glands on top of each kidney, and the pituitary is a pea-sized gland hanging from the base of the brain.
- Pancreas — elongated and leaf-like; lies behind and below the stomach, in the loop of the duodenum; its hormone-producing cells are the islets of Langerhans
- Thyroid — butterfly or H-shaped, with two lobes joined by a narrow bridge; lies in the front of the neck, on either side of the windpipe just below the voice box
- Adrenal glands — two small cap-shaped glands, one sitting on top of each kidney; each has an outer cortex and an inner medulla
- Pituitary — pea-sized and oval; hangs by a short stalk from the base of the brain, just below the hypothalamus
An everyday example. A visible swelling at the front of the neck, called goitre, is an enlarged thyroid — showing exactly where the gland lies.
The substance. The pituitary is called the master gland because it controls several other glands, yet it is itself controlled by the hypothalamus above it.
- Pancreas — elongated and leaf-like; lies behind and below the stomach, in the loop of the duodenum; its hormone-producing cells are the islets of Langerhans
- Thyroid — butterfly or H-shaped, with two lobes joined by a narrow bridge; lies in the front of the neck, on either side of the windpipe just below the voice box
- Adrenal glands — two small cap-shaped glands, one sitting on top of each kidney; each has an outer cortex and an inner medulla
- Pituitary — pea-sized and oval; hangs by a short stalk from the base of the brain, just below the hypothalamus
An everyday example. A visible swelling at the front of the neck, called goitre, is an enlarged thyroid — showing exactly where the gland lies.
The substance. The pituitary is called the master gland because it controls several other glands, yet it is itself controlled by the hypothalamus above it.
What do insulin, glucagon and thyroxine do in the body?
Insulin lowers blood sugar, glucagon raises it, and thyroxine controls the rate at which cells use energy, as well as growth and development.
Pancreas — the islets of Langerhans
- Beta cells secrete insulin
- Helps body cells take up glucose from the blood
- Makes the liver and muscles store glucose as glycogen
- Lowers blood sugar after a meal
- Alpha cells secrete glucagon
- Makes the liver break glycogen down into glucose
- Raises blood sugar between meals
Thyroid — thyroxine
- Contains iodine, so the thyroid needs iodine from food
- Controls the basal metabolic rate — how fast cells release energy
- Promotes growth and mental development in children
- Helps produce body heat
An everyday example. On a day you skip breakfast for an early tuition class, glucagon releases stored glucose so you can still concentrate.
The substance. Insulin and glucagon work in opposite directions, keeping blood sugar within a narrow range much as two people on a see-saw keep it level.
Pancreas — the islets of Langerhans
- Beta cells secrete insulin
- Helps body cells take up glucose from the blood
- Makes the liver and muscles store glucose as glycogen
- Lowers blood sugar after a meal
- Alpha cells secrete glucagon
- Makes the liver break glycogen down into glucose
- Raises blood sugar between meals
Thyroid — thyroxine
- Contains iodine, so the thyroid needs iodine from food
- Controls the basal metabolic rate — how fast cells release energy
- Promotes growth and mental development in children
- Helps produce body heat
An everyday example. On a day you skip breakfast for an early tuition class, glucagon releases stored glucose so you can still concentrate.
The substance. Insulin and glucagon work in opposite directions, keeping blood sugar within a narrow range much as two people on a see-saw keep it level.
What happens when insulin or thyroxine is secreted too little or too much?
Too little insulin causes diabetes mellitus and too much causes low blood sugar; too little thyroxine causes cretinism in children and myxoedema in adults, and too much causes exophthalmic goitre.
Insulin
- Hyposecretion — diabetes mellitus: high blood sugar, glucose in urine, frequent urination, great thirst and tiredness
- Hypersecretion — hypoglycaemia: blood sugar falls too low, causing weakness, sweating, trembling and in severe cases unconsciousness
Thyroxine
- Hyposecretion in children — cretinism: stunted growth and delayed mental development
- Hyposecretion in adults — myxoedema: low metabolic rate, puffy face and skin, sluggishness and weight gain
- Iodine deficiency — simple goitre: the thyroid enlarges because it cannot make enough thyroxine
- Hypersecretion — exophthalmic goitre: high metabolic rate, bulging eyes, weight loss, nervousness and a fast heartbeat
An everyday example. Iodised salt is sold throughout India to prevent iodine deficiency and simple goitre.
The substance. A goitre can form with too little thyroxine, because the gland enlarges while trying to make more — the feedback behind this appears in Part 2.
Insulin
- Hyposecretion — diabetes mellitus: high blood sugar, glucose in urine, frequent urination, great thirst and tiredness
- Hypersecretion — hypoglycaemia: blood sugar falls too low, causing weakness, sweating, trembling and in severe cases unconsciousness
Thyroxine
- Hyposecretion in children — cretinism: stunted growth and delayed mental development
- Hyposecretion in adults — myxoedema: low metabolic rate, puffy face and skin, sluggishness and weight gain
- Iodine deficiency — simple goitre: the thyroid enlarges because it cannot make enough thyroxine
- Hypersecretion — exophthalmic goitre: high metabolic rate, bulging eyes, weight loss, nervousness and a fast heartbeat
An everyday example. Iodised salt is sold throughout India to prevent iodine deficiency and simple goitre.
The substance. A goitre can form with too little thyroxine, because the gland enlarges while trying to make more — the feedback behind this appears in Part 2.
Exam tip
What earns full marks on glands, insulin and thyroxine?
Define terms precisely, give exact locations, and pair each hormone with its source, function and disorders.
- Endocrine versus exocrine — ducts, route of secretion, examples
- Locations — pancreas in duodenal loop, thyroid in neck, adrenals on kidneys, pituitary below brain
- Insulin from beta cells lowers sugar; glucagon from alpha cells raises it
- Thyroxine — iodine, metabolic rate, growth
- Disorders — say hypo or hyper, and child or adult where it matters
The trap. Confusing glucagon, the hormone, with glycogen, the stored carbohydrate. One letter changes the answer.
- Endocrine versus exocrine — ducts, route of secretion, examples
- Locations — pancreas in duodenal loop, thyroid in neck, adrenals on kidneys, pituitary below brain
- Insulin from beta cells lowers sugar; glucagon from alpha cells raises it
- Thyroxine — iodine, metabolic rate, growth
- Disorders — say hypo or hyper, and child or adult where it matters
The trap. Confusing glucagon, the hormone, with glycogen, the stored carbohydrate. One letter changes the answer.
Did you know
Why do people with diabetes often carry a sweet or glucose tablets?
It seems odd for someone with diabetes to keep a toffee in their pocket. The reason is the insulin itself.
An insulin dose that is too large, a missed meal or heavy exercise can push blood sugar too low. The person may suddenly feel shaky, sweaty and confused.
Eating glucose raises blood sugar within minutes, reversing the danger. The sweet is not a treat — it is an emergency fix for hypoglycaemia.
An insulin dose that is too large, a missed meal or heavy exercise can push blood sugar too low. The person may suddenly feel shaky, sweaty and confused.
Eating glucose raises blood sugar within minutes, reversing the danger. The sweet is not a treat — it is an emergency fix for hypoglycaemia.
Exam relevance
How do insulin and thyroxine lead into NEET Biology?
This is foundation work for Class 11 Chemical Coordination and Integration in NEET Biology.
What gets built on. The chapter names the alpha and beta cells of the islets, describes hyperglycaemia and diabetes mellitus, adds thyrocalcitonin from the thyroid, and explains how hormones act through receptors on or inside target cells, with protein hormones working through second messengers.
Question types. Match-the-column items pairing hormones with glands and disorders, and statement questions on hormone action.
The trap that costs marks. Diabetes mellitus involves insulin and sugar in urine; diabetes insipidus involves ADH and dilute urine without sugar. Options often swap them.
What gets built on. The chapter names the alpha and beta cells of the islets, describes hyperglycaemia and diabetes mellitus, adds thyrocalcitonin from the thyroid, and explains how hormones act through receptors on or inside target cells, with protein hormones working through second messengers.
Question types. Match-the-column items pairing hormones with glands and disorders, and statement questions on hormone action.
The trap that costs marks. Diabetes mellitus involves insulin and sugar in urine; diabetes insipidus involves ADH and dilute urine without sugar. Options often swap them.
Key takeaways
What must you be able to do from this part?
- Exocrine glands have ducts; endocrine glands are ductless and release hormones into blood
- Pancreas is a mixed gland
- Hormone: chemical messenger, small amounts, carried by blood, acts on a target organ
- Locations: pancreas in duodenal loop, thyroid in neck, adrenals on kidneys, pituitary below brain
- Insulin lowers blood sugar; glucagon raises it
- Thyroxine needs iodine, sets metabolic rate, supports growth
- Diabetes mellitus from too little insulin; hypoglycaemia from too much
- Cretinism and myxoedema from too little thyroxine; exophthalmic goitre from too much; simple goitre from iodine lack
Track your own blood sugar through one day in your head — breakfast, a long gap and dinner — and see if you can name which hormone is in charge at each point.
- Pancreas is a mixed gland
- Hormone: chemical messenger, small amounts, carried by blood, acts on a target organ
- Locations: pancreas in duodenal loop, thyroid in neck, adrenals on kidneys, pituitary below brain
- Insulin lowers blood sugar; glucagon raises it
- Thyroxine needs iodine, sets metabolic rate, supports growth
- Diabetes mellitus from too little insulin; hypoglycaemia from too much
- Cretinism and myxoedema from too little thyroxine; exophthalmic goitre from too much; simple goitre from iodine lack
Track your own blood sugar through one day in your head — breakfast, a long gap and dinner — and see if you can name which hormone is in charge at each point.